[sqlite] concatenation of row with NULLS suppresses all values

[Jim Dodgen]

drop table foo;
create table foo (x,y,z);
insert into foo values (1, null, null);
insert into foo values (2, null, null);
insert into foo values (3, 33, 333);
select x ||  "-" || y ||  "-" || z from foo;
whe I run the above select I only see the last row.
it looks as if a row has any nulls in the concatenation then all the values 
are suppressed.

is this the correct behavior?